Combined power and manually operated brake booster



Jan. 11, 1949.

Filed June 24, 1943 nip [3% 9 Vi i? J 6 7 26 52 45 J 14 4% I a? A 46 a j INVIiNTOR,

W. STELZER COMBINED POWER AND MANUALLY OPERATED BRAKE BOOSTER 2 Sheets-Sheet l Jan. 11, 1949, 2,458,803

comamrm POWER AND MANUALLY OPERATED BRAKE BOOSTER Filed June 24, 1943 W. STELZER 2 Sheets-Sheet 2 INVENTOR. W M

Patented Jan. 11, 1949 UNITED COMBINED POWER AND MANUALLY OPERATED BRAKE BOOSTER William Stelzer, East Orange, N. J. Application June 24, 1943, Serial No. 492,108

The invention relates to combined power and manually operated brake boosters and more particularly to a booster for a hydraulic braking system where the usual master cylinder or pressure producing device is incorporated in the booster unit.

It is well known that in conventional hydraulie brake systems the displacementof fluldafter a high pressure is reached is very small, whereas at thebeginning of the brake application when the pressure required is low the volume of fluid displaced to expand the brake shoes is considerable and varies depending on the adjustment of the clearance between the lining and the drum.

In order to transmit the necessary fluid to the wheelcylinders quickly, I have provided power means which are applied upon depression of the brake pedal by the operator, and which produce a fluid pressure sufilcient to apply the brakes. To obtain a quick stop requiring maximum hydraulic pressures a second stage piston is provided which takes over after the lower pressure has reached its maximum with the available power, the second stage piston producing a peak pressure transmitted to the wheel cylinders without appreciably increasing the displacement of the latter.

The object of the invention is to produce a simplified booster system lending itself particu- I larly for use with passenger cars where a construetion is required that can be manufactured cheaply without sacrificing any advantages.

Another object is to obtain a pressureproducing unit that is compact in construction, by utilizing a power booster of minimum size and providing special means for producing peak pressures.

A further object is to provide means to apply the brakes more quickly than this has been accomplished heretofore, to increase the safety of the brakes.

It is also the aim of this invention to decrease the required brake pedal travel by providing a power booster and a two stage pressure producing device.

Other objects and advantages of the invention will be apparent from the following detailed description considered in connection with the accompanying drawings submitted for the purpose of illustration and not intended to define the scope of the invention, reference being had for that purpose to the subjoined claims. -In the drawings, wherein similar reference characters 7 Claims. (Cl. fill-54.5)

refer to similar parts throughout the several views:

Fig. l is a sectional elevation of the improved hydraulic brake booster shown connected diagrammatically to a hydraulic braking system;

Fig. 2, a fragmentary sectional elevation of the device shown in Fig. 1, illustrating an optional construction;

Fig; 3, a sectional elevation of the improved hydraulic booster showing a modified construction, also shown connected diagrammatically to a hydraulic braking system. Before explaining in detail the present invention it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practised or carried out in various ways. Also it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not limitation.

Describing the invention now in detail, and referring to Fig. 1, there is shown a hydraulic brake booster unit serving as master cylinder also,

and comprising a housing -I having an auxiliary cylinder bore 2 in which the lower or primary stage pressure is produced, and a bore 3 in which the peak pressure is produced by means of plunger 4 having a seal 5 and being actuated by the conventional brake pedal 6 pivotally mounted to a structural member I of the vehicle, to which housing I may also be secured, as for instance at 8. Cylinder bore 2 accommodates power piston 9 whose larger end serves as a diaphragm plate in for diaphragm ll clamped thereto by means of ring l2, whereas the outer edge is clamped to housing I by means of cover l3. The enlarged end of housing I, piston plate I0, diaphragm H, and cover plate I3 form the main elements of an expansible chamber motor mechanism which furnishes the power to produce a hydraulic pressure in chamber M. The source of power consists of a source of lower pressure l5 and a source of higher pressure l6. I5 is prefer ably vacuum as received from the intake manifold of an internal combustion engine, and I6 atmospheric pressure. From the latter a flexible hose connection I! leads tovalve chamber I8 housing a ball I9 urged against its seat by a light spring 20. Low pressure source I5 is connected to chamber 2| of the expansible chamber motor mechanism and its pressure is communicated to chamber 22 via passage 23 past valve ball 24 urged away from its seat by a spring 25.

Piston 9 and plunger 4 are co-axial and adapted so that the'latter slides within piston 4 which also has a bore 24 housing a spring 21 held by a pickup ring 24 retained by a snap ring 24. Plunger 4 has a collar 30 against which valve actuating plate 3| is pressed by means of a conical spring 32 resting against collar 33 secured to plunger 4. Plate 3| merely serves as a doublearmed lever fulcrumed at 34 and having a pin 35 serving to unseat ball M. It is immaterial what shape plate 3| may have, but the central portion should have a hole through which the reduced end of plunger 4 may pass. The latter is guided in bearing or hub 36 of cover l3.

Piston 9 has a seal 31 retained by a spring 34 which urges piston a into its off" or idle position and also keeps seal 38 in a seated position."

Check valve 40 checks the flow of fluid from chamber 4 to reservoir 4|, where line 42 indicates the fluid level, but it permits the flow of fluid from 4| to chamber |4 through passage 43. A small hole 44 is in communication withbore 3. It is placed to be near seal when the booster is in the off" position. A passage 45 leads from chamber l4 to check valve 46 which checks the flow of fluid from bore 3 to chamber H but permits the flow of fluid vice versa. This check valve consists of a ball retained by a plug 41 also serving as a seat for return spring '44. Bore 3 is in communication with wheel cylinders 44 through fluid pressure transmitting line 54.

As illustrated in Fig. 2, a relief valve 4||- backed by a light spring may be used to close off port 44 in order to maintain a certain minimum pressure in the hydraulic circuit so that no air can enter the system.

In the modification shown in Fig. 3 the pressureproducing device or booster unit comprises a housing 5| having a high pressure chamber 52 and a co-axial auxiliary chamber 53 in which slides a power operated piston 54 provided with seals 55 and 56 and having a diaphragm plate 51 at one end which serves as a piston of an expansible chamber motor mechanism whose working chamber is designated by numeral 54 and is formed by diaphragm 54 clamped to housing 5| by a cover 54 and to diaphragm plate 51 by a clamping plate 4|. In chamber 52 slides a piston 62 having a piston rod 43 operated by manual power through brake pedal 44, link 45, and clevis 46. These manually operated elements are urged in a retractile or oil? position by conical spring 41. A sleeve 44 flts freely on piston rod 43 and is pressed against plate 4| by a spring 44. In the seated position it has a clearance with clevis 44 so that the manually operated elements maybe moved a suincient amount to allow lever ID to swing a certain distance to allow valve II to seat on seat 12 before clevis 44 comes in contact with sleeve 44. Lever or bell crank I4 is pivoted at 13 on a bracket extending from cover 44, and is arranged to hold valve 1| against seat 14 when the brake booster is in the "oil?" position as shown. For this purpose it presses against valve rod 15 sliding in insert 15 which has holes II to admit air to chamber 14 in communication with chamber 54 through passage 19. Valve II is urged against seat 12 by a light spring 44 of suflicient strength, however, to overcome the atmospheric pressure tending to keep valve ll seated on 14, the chamber in which spring 44 acts being open to a source of low pressure or suction 4| through line 42 in which a pressure modulator is interposed. This pressure modulator comprises a housing 43,

diaphragm 44, diaphragm plates 44, a piston rod 44 to which is secured an adjusting nut 41 for adjusting modulating spring 44 opposin the atmospheric pressure acting on diaphragm 44. cover 84 serving merely to secure the peripheral surface of diaphragm 44 to housing 43 to form a chamber 44. Fitting 4| serves as a valve seat for diaphragm plate 44 which shuts oil the supply of vacuum when the suction in chamber 40 is too great.

In order to transmit the hydraulic fluid from chamber 53 to wheel cylinders 44, a passage 42 and checlcvalve 43 are provided, allowing the flow of fluid via chamber 52. The pressure sensitive device comprising diaphragm 44 secured to housing 5| with cap 45 carrying a spring 44 serves to control check valve 43. Thus when the pressure in chamber 43 is relieved spring 44' acting against diaphragm plate 41 cracks check valve 93 open by means of a piston rod or operating pin 44 secured to said diaphragm plates.

The brake booster unit also comprises a fluid reservoir 44,. indicating the fluid level, and

I00 being a filler plug whose lower portion carries a valve IN to close off port hole I42 with a yielding force, governed by its ownweight. The purpose of this valve is to maintain a pressure greater than atmosphere to prevent the entry of air into the hydraulic system. Hole ||l3 provides communication between reservoir 44 and the space between seals 55 and 54 throughout the operation of the booster.

Having thus described the construction I .shall now explain the operation of the same. Assuming that the hydraulic braking system illustrated in Fig. 1 is in a released position as shown, and that the operator depresses foot pedal 6 to apply the brakes, piston 4 is moved towards the left to reduce the volume of chamber 3 and thereby force fluid to wheel cylinders or pressure receiving means 44. At the same time, since collar 30 of piston 4 moves to the left, plate or lever 3| moves withit due to the pressure of spring 32, though opposed by springs 24 and 25. The latter being weaker than spring 20, it yields first, allowing ball 24 to seat and to thereby close off the passage between vacuum chamber 2| and working chamber 22. The closing of valve 24, however, does not cause a change in pressure in chamber 22 as its pressure is still the same as that of chamber 2|. Further movement of lever 3| towards the left causes spring 2|) to be overpowered, whereby valve |4 cracks open. In cracking valve l4 plate 3| rocks on ball 24 because the latter is firmly seated and offers a resistance to further movement. Air is now permitted to flow from I4 through flexible hose past ball B into chamber 22 to urge piston plate Ill and hydraulic piston 4 towards the left totravel in unison with piston 4. Valves l4 and 24 are follow-up valves, causing plate It to travel at the same speed as piston 4, and regulating the fluid power directed to chamber 22 to accomplish this effect. Taking an example and assuming that plate l0 travels faster than piston 4, plate 3| would become retarded relative to valves I9 and 24. Ball i4 would close first, preventing further flow of fluid power to chamber 22 and retarding plate III. If the retardation of plate It is not suflicient ball- 24 becomes unseated to permit relief of pressure from chamber 22 into chamber 2|, thus stopping plate l4 entirely or allowing it to return until valve 24 is seated again.

Assuming now that the operator continues to depress pedal 4, movement of auxiliary piston 4 auaaos towards the left forces fluid from chamber l4 through passage 43, past check valve 49 and through line 39 to fluid pressure receivingmeans 49 to apply the brakes. The hydraulic pressure in chambers 3 and I4 are equal. After the operation has reached a stage where full power is applied to the expansible chamber motor mechanism, and where the power cannot be increased further, but pedal 4 ls further depressed by the operator with an increased force, piston 4 con-,

tinues its travel to force fluid to the wheel cylinders 49. Piston l4, however, remains stationary since the expansible chamber motor mechanism is incapable to increase the pressure in chamber I4 further. Consequently, check valve 44 is seated and prevents the higher pressure in chamber 3 to relieve itself into chamber l4. As piston 4 travels towards the left to produce a peak pressure, springs 21 and 32 are compressed. This movement, according to experience, is very small, so that collar 33 never comes in contact with plate 3|.

Supposing now that the operator releases pedal 6, piston 4 retracts towards the right due to spring 48 and the hydraulic pressure in chamber 3, on its way picking up plate 3i to allow valve I9 to close and 24 to open to relieve the pressure in chamber 22 so that piston 9 retracts in unison, helped by spring 38. A sucking action takes place in chamber l4 during the retractile movement, drawing fluid from reservoir 4|. It will be noted that no air can enter chamber 14 because chamber 2i is open to vacuum. When pistons 4 and necessary braking pressure. It will be apparent, however, that once the brake shoes have been set, the actual displacement of fluid from the cylinder 3 will be negligible in the building up of the necessary static pressure, and accordingly very slight movement of the piston 4 takes place after the brakes have set. Accordingly it will be apparent that due to the low initial pressure in the line 49, the piston 9 operates in the same manner as when the motor functions, it merely being necessary for the operator to exert somewhat greater pressure on the brake pedal.

The operation of the construction shown in Fig. 3 is similar to that of the embodiment shown in Fig. 1 except that the auxiliary piston 54 does not move in unison with piston 62 but travels independently and rapidly to force hydraulic fluid from chamber 53 to wheel cylinders 49 as soon as brake pedal '44 is depressed by the operator and clevis 99 has moved to the left sufliciently to allow lever 14 to turn a short distance until valve disc ii is seated on 12 by virtue of spring 90 to open the passage between source of vacuum 81 and chamber 58, effecting exhaustion of the latter. The hydraulic pressure in chamber 53 is increased depending on the strength or power of the expansible chamber motor mechanism whose working chamber 58 is connected to the vacuum, the

- other side of diaphragm 59 being open to atmos- 9 have reached their retracted or "01? position,-

port 44 is uncovered and the hydraulic fluid returning from wheel cylinders 49 is permitted to escape into reservoir 4|.

The device shown in Figure 1 is fully manually operative in the event of a failure of power in the vacuum motor. Assuming that the pedal is operated and the motor does not function, the pedal will move the piston 4 toward the left. Thispiston will start immediately to displace fluid through the line 50 to the brake cylinders, and very shortly after initial movement starts, the collar 30 will start to load the spring 21.

As is well known, most of the movement of fluid in the brake lines takes place to move the brake shoes into engagement with the ,drums, after which substantially static pressure is built up to secure the desired brake application. The initial displacement of fluid for the purpose stated takes place against relatively low resistance, and accordingly upon a relatively slight loading of the spring 21, movement will be imparted to the piston 9 to displace fluid from the chamber l4 through passage 45 and. thence past check valve 46 into the chamber 3 and on into the brake line 50. Inasmuch as there is a relatively free flow of fluid through the line 50 at this time, pressures will remain relatively equal in the cylinder 3 and chamber [4. Therefore it is necessary merely to build up suflicient loading of the spring 21 to operate the piston 9, whereupon both pistons 4 and 9 will displace fluid into .t he brake lines 44.

As soon as the brake shoes engage the drums, an immediate increase in pressurenoccurs in the line 59 and in the cylinder 3, whereupon the check valve 46 closes. Fluid will thereupon be trapped in the chamber i4 and the-piston 9 will cease to operate. pressed to a substantial extent, and accordingly it does not offer high resistance to-further manual movement of the piston 4. This piston continues,

to move by operation of the pedal to build up the phere. The hydraulic pressure produced in chamber 53 also acts on diaphragm 94 causing it to move downwardly against the pressure of spring 98 so that push rod 98 loses contact with ball 93. The force of the expansible chamber motor mechanism is Just suflicient to apply the brakes, so that the .brake shoes are fully in contact with the brake drums. To accomplish this, the modulator interposed in line 82 keeps the vacuum pressure constant regardless of fluctuations in source 8|. Chamber 99 contains the regulated fluid pressure, while the opposite side of diaphragm 84 is open to the atmosphere. Spring 84 is adjusted to yield when the pressure in chamber is too great, to connect the latter to, the source of vacuum when diaphragm plate lifts away from seat 9 I.

Assuming now that the brake shoes have expandedso that the resistance offered the fluid in wheel cylinders 49 is increased and the movement of auxiliary piston 54 consequently arrested, but that pedal 64 is further, depressed by the operator, then piston 52 is advanced into chamber 52 to force hydraulic fluid from there to wheel cylinders or hydraulic pressure receiving means 49. Check valve 93 is seated and prevents the flow of fluid from chamber 52 or wheel cylinders 49 to chamber 53. Thus a higher pressure is built up in chamber 52 and Wheel cylinders 49. Since the movement of piston 54 was very rapid after pedal 64 was operated, it may have advanced much faster than rod 63, thus establishing a' gap or clearance between sleeve 88 and clevis 66. The movement of piston 62 to provide a peak pressure may be smaller than said gap or clearance so that clevis 66 may not come in contact with sleeve 68 at any time during the operation. However, if the movement of brake pedal 6 is very rapid the clearance between clevis 66 and .sleeve 69 when piston 54 comes to rest may be The spring 2-! will not have been co msmall so that upon further depression of pedal 6 spring 89 is compressed, which does not change thqoperation of the brakes in any manner. The purpose for spring '69 is to serve as means for moving-piston 54 in case of failure of the source of power, when piston 54 would be moved .by

7 thermal power through lever ll, clevis it, sleeve 8!, and spring 6.. At a point where the brakes are applied spring 69 would compress and piston 62 advance alone.

Assuming now that the operator releases brake pedal 84, piston 62 is permitted to retract to the "of! position, where clevis 8i actuates lever ll which raises valve II to close off the supply of vacuum and lets air through holes TI into chamber 58 to equalize the pressures between the two sides of diaphragm 59 whereby auxiliary piston 5| starts its retractile movement while diaphragm 84 due to the relief of pressure in chamber 53 is raised by spring 96 to crack check valve -93 so that hydraulic fluid may return from wheel cylinders 49 to chamber 53. In the o position port I02 is uncovered by cup 5 to allow excess pressure to relieve itself into reservoir Iill.

Having thus described the invention, I claim:

1. In a hydraulic braking system having actu ating cylinders to expand the brake shoes, in combination, a pressure producing device comprising a chamber and a manually operated piston therein to force fluid to said actuating cylinders, an auxiliary piston in a separate chamber to produce a hydraulic pressure, a power motor to operate said auxiliary piston, fluid pressure transmitting means leading from said separate chamber to said actuating cylinders, check valve means interposed in said fluid pressure transmitting means arranged to permit the flow of fluid from said separate chamber to said actuating cylinders but not in the opposite direction, and resilient means interposed between a said manually operated piston and said auxiliary piston to tend to operate the latter upon operation of said manually operated piston.

2. In a hydraulic braking system having hydraulic pressure receiving means to actuate the brakes, in combination, a pressure producing device comprising a chamber and a manually operated piston therein to force brakeifluid to.said fluid pressure receiving means, manual operating means therefor, an auxiliary piston in a separate chamber to produce a hydraulic pressure therein, an expansible chamber motor mechanism to operate said auxiliary piston, fluid pressure transmitting means leading from said separate chamber to said hydraulic pressure receiving'means, a check valve interposed in said fluid pressure transmitting means to allow fluid to pass from said separate chamber to said hydraulic pressure receiving means, valve means responsive to the movement of said manual operating means to control said expansible chamber motor mechanism to operate said auxiliary piston, and resilient means interposed between said manually operated piston and said auxiliary piston to tend to operate the latter upon operation of said manually operated piston.

3, In a hydraulic braking system having hydraulic pressure receiving means to actuate the brakes, in combination, a pressure producing device comprising a chamber and a manually operated piston therein to force hydraulic fluid to said hydraulic pressure receiving means, lever means for manually operating said piston, an auxiliary piston in a separate chamber to produce a hydraulic pressure thereiman expansible chamber motor mechanism to operate said auxiliary piston, fluid pressure transmitting means from said separate chamber to said hydraulic pressure receiving means, a check valve interposed in said fluid pressure transmitting means to prevent the return of fluid from said hydraulic pressure re- Ill ceiving means to said separate chamber, a source of power, valve means to direct power to and from said expansible chamber motor mechanism, means responsive to the application of said lever means to operate said valve means to direct power to said expansible chamber motor mechanism,

said manually operated piston being capable of continuing its stroke after said auxiliary piston has stopped due to too great resistance, and resilient means interposed between said manually operated piston and said auxiliary piston to tend to operate the latter upon operation of said manually operated piston.

4. In a hydraulic braking system having hydraulic pressure. receiving means to actuate the brakes, in combination, a pressure producing device comprising a pressure chamber, a manually operated piston therein to force fluid to said hydraulic pressure receiving means, manually operated lever means to actuate said piston, an auxiliary chamber, a power operated piston in said auxiliary chamber, a check valve intermediate said auxiliary chamber and said pressure chamber arranged to allow flow of fluid from said auxiliary chamber to said pressure chamber but to check the flow of fluid in the opposite direction, yielding means interposed between said manually operated piston and said power operated piston to urge said power operated piston to travel in unison with said manually operated piston, means urging to open said check valve, and means responsive to the hydraulic pressure in said auxiliary chamber to oppose said means that urges to open said check valve, whereby said check valve is opened when the hydraulic pressure in said auxiliary chamber is reduced.

5. In a hydraulic braking system having hydraulic pressure receiving means to apply the brakes, in combination, a pressure producing device comprising a first pressure chamber, a manually operated piston therein, manuually operated means to actuate said piston, an auxiliary pressure chamber in axial alignment with said first pressure chamber, a piston in said auxiliary chamber. a fluid power motor mechanism to actuate said piston in said auxiliary pressure chamber, fluid pressure transmitting means from said auxiliary chamber to said hydraulic pressure re ceiving means, a check valve interposed to check the flow of fluid from said hydraulic pressure receiving means to said auxiliary pressure chamber, a source of fluid pressure, a valve means to direct fluid pressure to said fluid power motor mechanism, means to open said valve means upon initial actuation of said manually operated means to energize said fluid power motor mechanism to urge said piston in said auxiliary pressure chamber to force hydraulic fluid to said hydraulic pressure receiving means at a rate inde endent of said manually operated piston, and resilient means interposed between said manually operated means and said second named piston to tend to operate the latter upon operation of said manually operated means.

6. In a hydraulic braking system having wheel cylinders and a manually operable element, a pair of cylinders in axial alinement, a piston operable in each cylinder, said pistons being coaxial and one surrounding the other, the inner piston being of smaller area than the outer piston, means for connecting the cylinder of the smaller piston to said brake cylinders, check valve controlled means for supplying fluid from the cylinde of the larger piston to the brake cylinders, mea for positively transmitting movement of said manually operable element to said smaller piston, power means for eflecting movement of the larger piston, a control device for said power means operable upon initial operation or said manually operable element, and resilient means arranged to transmit to the larger piston forces delivered to the smaller piston by said manually operable element.

'1. Apparatus constructed in accordance with claim 6 wherein said power means comprises a diflerential fluid pressure motor having a pressure responsive structure, said control device comprising control valves carried by said structure, and lever means for eflectlns operation of said valves upon initial operation of said manually operable element.

WILLIAM STELZER.

10 REFERENCES" CITED The following references are of record in the tile of this patent:

UNITED STATES PATENTS 

